Suherman, S, Ali Hanafiah Rambe, and Agustiar Widodo Tanjung. 2018. “Underground Radio Propagation on Frequency Band 97 Mhz – 130 Mhz”. International Journal of Engineering & Technology 7 (3.2): 722-26. https://doi.org/10.14419/ijet.v7i3.2.15352.